The walrus has been added to the growing list of animals that seem to prefer using one hand, or flipper, over the other.

The ivory-tusked sea mammal tends to use its right flipper to forage for clams on the sea bed, say scientists.

Anatomical studies confirm that the bones in the walrus' right limb are longer than those in the left - the same phenomenon seen in right-handed people.

The Danish, Swedish and Greenland researchers report their discovery in the online journal BMC Ecology.

Long mystery

Handedness - preferring one side of the body to the other for certain tasks - has been found in chimps, monkeys and even crows, so it is perhaps not surprising that it should be found in an aquatic mammal.

Some people say handedness developed in primates from tool manipulations but this cannot be the driving force

Nette Levermann, University of Copenhagen

Handedness has long been studied in the human population, but, after more than 150 years of research, scientists are still divided over why right-handers vastly outnumber left-handers.

It seems to be something to do with the way the brain is organised into two halves, allowing one side to specialise over the other for certain functions such as language.

Some have postulated that handedness arose in primates and is somehow related to the development of speech or tool-making skills.

But the latest research casts doubt on this, as did the recent discovery that a species of Pacific crow uses the right side of its beak to craft leaves into tools for catching insects.

"Some people say handedness developed in primates from tool manipulations", lead researcher Nette Levermann, of the University of Copenhagen, told BBC News Online, "but this cannot be the driving force because it is found in walruses and, to a certain extent, in humpback whales and catfish."

Harbour seals

Observations of humpback whales show they use either the right or left side of the jaw when snatching prey.

A walrus foraging on the sea bed in North Greenland

Harbour seals in the waters off Scotland also seem to show handedness, says Mike Fedak of the UK's Sea Mammal Research Unit at the University of St Andrews.

They tend to use their right flipper when engaged in the task of beating at the sand to scare the sand eels they feed on out of hiding.

The nails on the right flipper also get worn down more quickly than the ones on the left.

"It is not surprising to me that handedness appears in bilaterally symmetrical animals," he said.

"Any task that involves only using one limb rather than both might be learned favourably on one side."